Hydraulic Accumulators

Get guidance and suggestions from DTA for your hydraulic accumulators to ensure they are properly maintained and safe to use.

A hydraulic accumulator stores fluid under pressure and can serve a number of functions within a hydraulic system. Its an item that can provide years of trouble-free service.

Accumulators can take a specific amount of fluid under pressure and store it. The fluid is then released when its required to perform a specific task in the hydraulic system. Accumulators can provide several functions, such as:

• Energy storage
• Compensation of leakage oil
• Compensation of temperature fluctuations
• Emergency operation
• Cushioning of pressure shocks which may occur at sudden switching of the valves
• Dampening vibrations
• Swell compensator (in marine hydraulics)

Adding an accumulator to a hydraulic system offers a number of advantages. In addition, it results in substantial energy savings and an increased system lifespan. Applications that require a lot of power for limited periods of time can benefit most from the use of accumulators.

• Possibility of smaller pumps
• Lower installed power
• Less heat produced
• Simple maintenance and installation
• Increased service lifetime
• Immediate availability
• Unlimited storage life
• No fatigue
• No inertia

Applications that utilise large flows at high speeds may use accumulators for energy storage. When required, the accumulator pushes fluid into the hydraulic circuit to add to the pump flow. When the actuators in the hydraulic system are not in motion, the accumulator will refill. Accumulators can also operate as energy sources during normal operation of the system (i.e. cushioning).

Accumulators that are weight- or spring-loaded can also be used in industrial applications. For example, a gas-pressurised hydro-pneumatic accumulator, which has a gas-tight separating element, is most commonly used. Without a separating element, the fluid can absorb gas. The gas used is nitrogen; this prevents danger of explosion in case of leakage of the bladder, diaphragm or piston.

How DTA Can Help You:

DTA supplies hydraulic accumulators from several renowned vendors. Along with our strong knowledge of the hydraulic market, we can also provide you guidance and suggestions to ensure all accumulators are properly maintained and safe to use.

Note that accumulators are pressure vessels and, as such, are manufactured, tested and certified according to statutory standards.

Different Types of Hydraulic Accumulators

Accumulators basically comprise of two compartments: one of the compartments is filled with gas; the other compartment, which is connected to the hydraulic circuit, is filled with fluid. The accumulator shell is made of carbon steel, stainless steel or aluminium. Depending on separating elements, we can distinguish three types of hydraulic accumulators:

• Bladder accumulators
• Diaphragm accumulators
• Piston accumulators

We also provide a variety of accumulator accessories for your convenience and safety. Note that the most common type of accumulator employed in modern hydraulic systems is the nitrogen gas-loaded type.

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A bladder accumulator is the most commonly used hydro-pneumatic accumulator. The bladder is filled with nitrogen and fitted in a welded or forged steel pressure vessel. The bladder is made of an elastic material (elastomer), e.g. rubber. The gas pre-charge pressure can be adapted via the gas inlet/outlet valve on top of the bladder accumulator.

If the bladder accumulator is mounted vertically or at an angle, the gas side must always be on top. When the pressure drops, the compressed gas in the bladder expands and pushes the stored fluid into the hydraulic circuit. At zero pressure, the bladder may be pushed out of the pressure vessel. To prevent this, a spring-loaded valve is provided on the fluid side.

The bladder accumulator is used when a high power output is required. Specially designed bladder accumulators are capable of operating at maximum pressures of up to 1,000 bar. The gas volume and effective hydraulic volume is medium, ranging from 0.5 l to 450 l.

Note that by combining several accumulators in a hydraulic sub-system, you can reach any capacity you would like by just adding extra accumulators to that sub-system.

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These accumulators have a rubber plate or diaphragm as the separating element. This element is welded or screwed together between two spherical shells (or compartments). The compartment above the diaphragm is filled with nitrogen. The compartment below is directly connected to the hydraulic circuit. Diaphragm accumulators are useful if the required fluid storage capacity is low (i.e. 4 litres or less).

Diaphragm accumulators have most of the advantages of bladder-type units, but can handle gas compression ratios of up to 8:1. However, they are limited to smaller volumes, and their performance can sometimes be affected by gas permeating across the diaphragm.

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Piston accumulators use pistons as separating elements. They can handle much higher gas compression ratios (up to 10:1) and flow rates as high as 215 litres (57 gallons) per second. However, the piston inside the accumulator causes internal friction that negatively affects reaction speed (i.e. has slower response times greater than 25 ms).

Piston accumulators also require a higher level of fluid cleanliness than bladder units. Piston accumulators are used for very large fluid storage requirements of up to 2,500 litres at very high pressures (up to 1,000 bar).

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Contact DTA for your accumulator accessory needs.

Accumulators are pressure vessels and therefore must be handled with care. To mount the accumulator safely, special fixing elements are available. Moreover, an accumulator should never be installed without a safety and shut-off control block.

Special testing devices are available to test pressure of the nitrogen gas. Testing should be carried out at least once a year. Mobile nitrogen charging devices are available to replenish the gas or change the prefilled pressure.

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